The present invention relates to data medium networks, in particular, local and wide area data medium network monitors and taps.
Previously, the most widely used approach for monitoring network data was to interpose a network hub 12 and connect a system or network monitor 40 to hub port 16 to monitor the network data, as shown by the exemplary block diagram 10 of FIG. 1. Firstly, the system must have a spare port or tolerate the loss of a port to permit system analysis. In addition, the hub will reject data containing errors and/or will mask out data errors. When a spare port is made available, the interposition of the data hub port introduces significant network data delays, typically in excess of 90 serial data bits, which does not provide a sufficiently accurately or transparent data connection. In many instances, such degradation makes network monitoring unacceptable.
Such data delay limitations experienced by hub and other prior data translation devices are, in large part, a result of internal transfer data from the incoming media serial format to an internal parallel format for buffering or processing, and back to the serial format for retransmission. The well established building blocks used in many such systems consist of a an integrated circuit, e.g. part # DP83223, which provides the necessary electrical signalling and media state, while a second subsequently connected integrated circuit, e.g. part # DP83240, recovers the clock signal from the incoming signal, decodes or descrambles the NRZ, MLT3 or other cipher format encrypted signal and provides a plaintext data signal in a 4-bit parallel standard. The plaintext parallel data is then received by a buffer or processor provided by a variety of integrated circuits. For hub configurations, similar parallel data paths are provided.
Moreover, when attached to a spare port of a hub, the data flow of the channels, e.g. 21, 23, 25, attached to corresponding ports cannot be isolated, so that data is co-mingled and collisions occur, preventing the system monitor or network analyzer from accurately monitoring any channel. Furthermore, data presented to the system monitor via a spare port is only Half-Duplex, which does not monitor a Full-Duplex channel. The hub works in a contention mode and will only allow data to be received from one port to be presented to the monitor port. If any other port attempts to transmit data, such data will be suppressed and the data on the monitor port will be distorted or suppressed in order to indicate a collision event. Also, the system monitor or network analyzer cannot interrupt a single channel data flow to send diagnostic data, or reliably monitor the response of the equipment connected to that channel without incurring interference from data collisions as previously discussed.
As demonstrated by the widespread adherence to the parallel data format by integrated circuit and equipment designers, the limitations imposed on the data flow by translation from and to the parallel format are generally accepted as unavoidable, and thus the performance of data translation equipment is only marginally improved.
The apparatus and method according to the present invention provide a serially buffered network tap including physical layer devices which provide the necessary media interfacing and clock recovery and a serial stream of data to a serial data multiplexer which provides bit synchronization with a minimal data bit delay, typically 5 bits.
Further, the present invention provides a data monitor system including the tap and a network monitor or system analyzer provides virtually transparent network channel monitoring of the Full-Duplex data flow thereon. Moreover, according to the present invention, the tap provides selective access to the network data flow in either direction according to network monitor or system analyzer control for network system diagnosis, etc. Also, the system monitor or network analyzer can selectively insert data in either direction to provide complete diagnostic testing of the channel.
Having recognized the desirability, and providing the apparatus and method to provide data translation according to the present invention, a total typical translated data delay time of 10 bits or less is achieved. When compared to the typical 4-bit parallel data systems data typical delay of at least 45 bits, the apparatus of the present invention provides a significant improvement.